In the IPA chart，the sound segments are grouped into CONSONANTS and VOWELS，which will be discussed in detail in the next section．The consonants are then divided into pulmonic and non-pulmonic consonants：PULMONIC sounds are produced by pushing air out of the lungs，as in most circumstances， while NON-PULMONIC sounds are produced by either sucking air into the mouth，in the case of clicks，or closing the glottis and manipulating the air between the glottis and a place o f articulation further forward in the vocal tract， as is the case of implosives and ejectives．The vowels are shown their relevant positions in a cross-sectional diagram o f the oral cavity．The“other symbols”are actually a group of consonants that involve more than one place or manner o f articulation，which cannot be placed into one o f the slots in the consonant chart．The DIACRITICS are additional symbols or marks used together with the consonant and vowel symbols to indicate nuances of change in their pronunciation．The suprasegmentals are used to represent stress and syllables， whereas the last group o f symbols is used to show tonal di fferences and intonation patterns．2．2 Consonants and VowelsIn the description o f sound segments，a basic distinction is made between consonants and vowels．Consonants are produced“by a closure in the vocal tract． or by a narrowing which is SO marked that air cannot escape without producing audible friction”．By contrast-a vowel is produced without such“stricture”SO that“air escapes in a relatively unimpeded way through the mouth or nose” （Crystal，1 997：1 54）．The distinction between vowels and consonants lies in the obstruction of airstream．As there is no obstruction o f air in the production o f vowels，the description of the consonants and vowels cannot be done along the same lines．